A typical vane-type camshaft phaser for changing the phase relationship between a crankshaft and a camshaft of an internal combustion engine generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is selectively supplied to one of the advance and retard chambers and vacated from the other of the advance and retard chambers by a phasing oil control valve in order to rotate the rotor within the stator and thereby change the phase relationship between the camshaft and the crankshaft. One such camshaft phaser is described in U.S. Pat. No. 8,534,246 to Lichti et al., the disclosure of which is incorporated herein by reference in its entirety and hereinafter referred to as Lichti et al.
While the camshaft phaser of Lichti et al. may be effective, the camshaft phaser may be parasitic on the lubrication system of the internal combustion engine which also supplies the oil for rotating the rotor relative to the stator, thereby requiring increased capacity of an oil pump of the internal combustion engine which adds load to the internal combustion engine. In an effort to reduce the parasitic nature of camshaft phasers, so-called cam torque actuated camshaft phasers have also been developed. In a cam torque actuated camshaft phaser, oil is moved directly from the advance chambers to the retard chambers or directly from the retard chambers to the advance chambers based on torque reversals imparted on the camshaft from intake and exhaust valves of the internal combustion engine. The torque reversals are predictable and cyclical in nature and alternate from tending to urge the rotor in the advance direction to tending to urge the rotor in the retard direction. The effects of the torque reversals on oil flow are known to be controlled by a valve spool positioned by a solenoid actuator. Accordingly, in order to advance the camshaft phaser, the valve spool is positioned by the solenoid actuator to create a passage with a first check valve therein which allows torque reversals to transfer oil from the advance chambers to the retard chambers while preventing torque reversals from transferring oil from the retard chambers to the advance chambers. Conversely, in order to retard the camshaft phaser, the valve spool is positioned by the solenoid actuator to create a passage with a second check valve therein which allows torque reversals to transfer oil from the retard chambers to the advance chambers while preventing torque reversals from transferring oil from the advance chambers to the retard chambers. One such camshaft phaser is described in U.S. Pat. No. 7,000,580 to Smith et al. However, packaging of the first check valve and the second check valve within the camshaft phaser, particularly packaging check valve springs needed for biasing check valve members of the first check valve and the second check valve toward respective check valve seats, results in added complexity.
What is needed is camshaft phaser which minimizes or eliminates one or more the shortcomings as set forth above.